The BBC has admitted hiring a notorious private investigator who was convicted of supplying newspapers with illegally obtained private information about celebrities and public figures.

The corporation said it had commissioned Steve Whittamore, whose targets have included the parents of murdered schoolgirls Milly Dowler and Sarah Payne, on one occasion in 2001.

His brief was help to track down an unnamed convicted paedophile who BBC journalists working on an unknown programme believed was planning to travel to Britain, and the public broadcaster says his work was justifiable.

The BBC said: "In this case a private investigator was commissioned in 2001 to track down a convicted paedophile who was believed to be returning to the United Kingdom.

"The BBC has provided the details of this matter to Ofcom who confirmed that they are satisfied with our explanation that this was warranted in the public interest and they are not taking any further action."

The corporation refused to release more detailed information, but it is thought to be planning to give full details of the case to the Leveson inquiry. Mark Thompson, the BBC director general, expects to be called before the inquiry in the new year.

Whittamore was at the heart of a network of corrupt officials and "blaggers" responsible for obtaining information such as ex-directory phone numbers, car registrations and criminal records. In 2005 he pleaded guilty to breaches of the Data Protection Act and received a two-year conditional discharge.

Until now it was thought that Whittamore's clients were limited to 32 newspapers and magazines, from which 305 journalists made in excess of 17,000 requests for information. But after questioning from Ofcom, the broadcasting regulator, the BBC has admitted to being a customer of the private investigator.

Logs kept by Whittamore – and held by the Information Commissioner's Office in the wake of his prosecution – are understood to show the words "airline check" and "£150" recorded against the corporation's name. It is believed to be the only reference to the BBC using the private investigator, information which has now been shared with Ofcom.

There is no evidence that Whittamore acted illegally in this instance. However, a spokesman for the Information Commissioner's Office said: "Unlawfully obtaining or accessing personal data, such as airline passenger records, without the consent of the data controller is a criminal offence under section 55 of the Data Protection Act 1998. This includes the practice known as 'blagging' where an individual obtains someone's personal information, usually by deception."

There is also a public interest defence against such breaches of the Data Protection Act, cited in this instance by the BBC.

Earlier this month the BBC revealed that an internal review had cleared its journalists of any illegal practices, but conceded that private investigators were sometimes used. The subject was discussed at the BBC Trust meeting on 24 October and its minutes noted that "the BBC does use private investigators occasionally, most commonly for surveillance or security services (to ensure the safety of journalists or to check the safety or carry out a 'recce' of a location where filming is taking place) and to obtain the whereabouts or identity of individuals who are the subjects of significant public interest programmes."

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